Hard carbon is considered as the most prospective anode material for sodium ion batteries. However, the loss of plateau capacities at high rates, arising from large electrochemical polarization, causes rapid degradation in the rate performances of batteries. In this work, we found that the plateau capacities of hard carbon at high rates could be significantly enhanced in ether-based electrolytes.

Rechargeable sodium-ion batteries are promising next-generation energy storage devices due to the low cost and rich natural abundance of Na. However, it is still a great challenge to suppress phase changes of cathode materials in the high-voltage region. Unlike P-type single-phase composites, herein we present a facile strategy for preparing P3/P2-type biphasic layered Na0.66Co0.5Mn0.5O2, namely, integrating P2 into P3-layered materials. The crystalline structure of Na0.66Co0.5Mn0.5O2, which was investigated by ex situ X-ray diffraction, was well maintained over long cycling in a high-voltage range. Taking advantage of their structural stabilization, Na0.66Co0.5Mn0.5O2 cathode materials displayed remarkably steady discharge capacity at high rates. With outstanding structural flexibility and electrochemical performance, Na0.66Co0.5Mn0.5O2 would stimulate the development of sodium-ion batteries.

•We successfully synthesized Y-doped LiCoPO4 via a citric acid-based sol–gel route.•Y-doping can optimize the morphology and crystal microstructure of LiCoPO4.•Y-doped LiCoPO4 presents a higher discharge capacity and better cyclic stability.Pure and Y-doped LiCoPO4 samples are prepared by a citric acid-based sol–gel route followed by heat treatment. X-ray diffraction, scanning electron microscopy and charge–discharge tests show that a small amount of Y3 + doping can significantly improve the capacity delivery and cycling properties of LiCoPO4 without affecting its structural properties. Y-doped LiCoPO4 (x = 0.01) cathode material presents a high discharge capacity of 154.3 mAh g− 1 (0.1 C) at room temperature. Cyclic voltammetric and electrochemical impedance spectra tests disclose that the Li-ion diffusion, the reversibility of lithium extraction/insertion, electrical conductivity and electrochemical reaction are significantly improved in Y-doped LiCoPO4.

In order to inhibit the decomposition of the electrolytes and improve the performance of Li3V2(PO4)3 cathode materials at high potentials, we propose a conducting polymer coating method by the in situ electropolymerization of thiophene which was added to conventional organic electrolytes. The formation of polythiophene film on Li3V2(PO4)3 surface was demonstrated by high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. Polythiophene-coated Li3V2(PO4)3 cathode materials exhibited higher reversible charge/discharge capacity and better rate performance. Electrochemical impedance spectroscopy indicated that the addition of thiophene decreased the decomposition of the electrolytes on the cathode surface and improved the electronic conductivity of Li3V2(PO4)3, allowing Li+ ions in Li3V2(PO4)3 to deintercalate/intercalate more smoothly.Graphical abstractHighlights► In situ electropolymerization of thiophene in the conventional organic electrolyte improved Li3V2(PO4)3 cathode materials. ► The cathode materials exhibited higher reversible capacity and better rate performance. ► The addition of thiophene improved the deintercalation/intercalation of the third Li+ ion at high electrode potentials.

LiCoPO4/C composites were synthesized through a sol–gel route, followed by thermal treatment. X-ray diffraction patterns demonstrate the phase formation of LiCoPO4. Scanning electron microscopy and transmission electron microscopy show the network structure of LiCoPO4/C composites with the grain size ranging from 240 to 350 nm. For the electrochemical measurements of LiCoPO4/C composites in Li test cells, thiophene was added as an electrolyte additive. After 30 cycles, the discharge capacity of LiCoPO4/C composites was 92.8 mAh g−1 with 68% capacity retention; the improved cyclic performance was attributed to the combination of the network structure LiCoPO4/C composites and the thiophene addition to the electrolyte.Highlights► LiCoPO4/C composites were synthesized through a sol–gel method, followed by thermal treatment. ► Thiophene was added to the conventional electrolyte as an additive. ► Polymerized thiophene film and carbon coating protect electrolyte from decomposition. ► Combination of C coating and thiophene electrolyte additive is effective for cyclic stability.

Lithium difluoro(oxalato)borate (LiDFOB) was investigated as an electrolyte additive for high-voltage lithium-ion batteries in order to decrease the decomposition of the electrolyte. As a typical high-voltage cathode material, LiCoPO4 was tested in the LiDFOB-containing electrolyte, exhibiting higher reversible charge/discharge capacity and better cyclic stability. The effect of LiDFOB on the formation of a stable interphase film was investigated through cyclic voltammetry and X-ray photoelectron spectroscopy. LiDFOB was helpful to form a stable interphase film and passivate the cathode surface; therefore, the decomposition of the electrolyte was inhibited accordingly.

A very simple and rapid method for synthesizing LiCoPO4/C nanocomposite has been developed via microwave heating. X-ray diffraction confirmed that nanosized olivine LiCoPO4 was successfully synthesized. Scanning electron microscopy and transmission electron microscopy verified that LiCoPO4 displays small powders with an average size of ∼150 nm and is also coated with uniform amorphous carbon film of ∼10 nm in thickness. Compared with pure LiCoPO4, LiCoPO4/C composite presented enhanced electrochemical Li-ion intercalation performances. Cyclic voltammetric and electrical tests disclosed that the Li-ion diffusion, the reversibility of lithium extraction/insertion and electrical conductivity were significantly improved in LiCoPO4/C composite.

Room temperature ionic liquid (RTIL) was prepared on basis of N-methyl-N-butylpiperidinium bis(trifluoromethanesulfonyl)imide (PP14TFSI), which showed a wide electrochemical window (−0.1–5.2 V vs. Li+/Li) and is theoretically feasible as an electrolyte for batteries with metallic Li as anodes. The addition of vinylene carbonate (VC) improved the compatibility of PP14TFSI-based electrolyte towards lithium anodes and enhanced the formation of solid electrolyte interphase film to protect lithium anodes from corrosion. Accordingly, Li/LiFePO4 cells initially delivered a discharge capacity of about 127 mAh g−1 at a current density of 17 mA g−1 in the ionic liquid with the addition of VC and showed better cyclability than in the neat ionic liquid. Electrochemical impedance spectroscopy disclosed that the addition of VC enhanced Li-ion diffusion and depressed interfacial resistance significantly.

Hard carbon is considered as the most prospective anode material for sodium ion batteries. However, the loss of plateau capacities at high rates, arising from large electrochemical polarization, causes rapid degradation in the rate performances of batteries. In this work, we found that the plateau capacities of hard carbon at high rates could be significantly enhanced in ether-based electrolytes.

Rechargeable sodium-ion batteries are promising next-generation energy storage devices due to the low cost and rich natural abundance of Na. However, it is still a great challenge to suppress phase changes of cathode materials in the high-voltage region. Unlike P-type single-phase composites, herein we present a facile strategy for preparing P3/P2-type biphasic layered Na0.66Co0.5Mn0.5O2, namely, integrating P2 into P3-layered materials. The crystalline structure of Na0.66Co0.5Mn0.5O2, which was investigated by ex situ X-ray diffraction, was well maintained over long cycling in a high-voltage range. Taking advantage of their structural stabilization, Na0.66Co0.5Mn0.5O2 cathode materials displayed remarkably steady discharge capacity at high rates. With outstanding structural flexibility and electrochemical performance, Na0.66Co0.5Mn0.5O2 would stimulate the development of sodium-ion batteries.